Pregame: N.L. Central leaders at Petco

Andrew Cashner #34 of the San Diego Padres pitches during the first inning of a baseball game against the New York Yankees at Petco Park on August 2, 2013 in San Diego, California. (Denis Poroy/Getty Images)

Andrew Cashner #34 of the San Diego Padres pitches during the first inning of a baseball game against the New York Yankees at Petco Park on August 2, 2013 in San Diego, California. (Denis Poroy/Getty Images)

And for the second time in a week, the Padres halted the rehab assignment of center fielder Cameron Maybin with Triple-A Tucson and brought him back to San Diego for a further evaluation of his right knee. The Padres hinted they could seek a second opinion on Maybin, who has been on the disabled list since injuring the PCL in his right knee while diving for a catch in Colorado on June 9.

The Padres also announced that outfielder Kyle Blanks, who was been on the disabled list since July 12 with Achilles tendinitis, could begin a rehab assignment with Triple-A Tucson by next weekend.

Padres manager Bud Black also reduced the odds of Carlos Quentin returning this season to “50-50.”

“Right now, he’s not making the progress we had hoped for,” Black said of Quentin, who last played on July 30 after appearing in 30 of the previous 32 games. Quentin’s right knee has not responded to three injections of a bone lubricant in his right knee.

Boxberger, 25, was 2-4 with a 3.67 earned run average in 41 appearances covering 56 1/3 innings for Tucson. He had three previous stints with the Padres this season and was 0-1 with 4.00 ERA in six appearances covering nine innings. He was 0-0 with a 2.60 ERA in 24 appearances with the Padres in 2012.

O’Sullivan, 25, was 0-1 with a 3.96 ERA in seven appearances (three starts) covering 25 innings since being promoted from Tucson on July 12. He and Tim Stauffer gave the Padres two long relievers in the bullpen since he made his last start against Cincinnati on July 29.

Meantime, the Padres flew to San Diego from Pittsburgh after losing a 16-inning game to Arizona Sunday. It marked the second straight season that the Pirates opened a three-game series at Petco Park after playing an extra-inning game in a different time zone. Last season, Pirates lost at Petco Park the day after a 19-inning game in St. Louis.

The Pirates lead the National League Central. But in each of the past two seasons, the Pirates fell under .500 after struggling against the Padres. The Padres won five of six games against the Pirates last year and swept them at Petco Park. In 2011, the Padres were 4-2 against the Pirates.

Pirates outfielder Andrew McCutchen is a candidate for the National League Most Valuable Player Award. He is hitting .318 with 17 homers, 69 RBIs and a .391 on-base percentage and ranks in the top 10 of most N.L. statistical categories. Third baseman Pedro Alvarez has 30 homers and 81 RBI.